[
https://issues.apache.org/jira/browse/HDFS-2179?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13079530#comment-13079530
]
Todd Lipcon commented on HDFS-2179:
-----------------------------------
Yes, sorry for not running test-patch before. I just ran it and it pointed out
that I was missing the license on one of the new test files as well. Aside from
that, it passes.
As for why it goes in the NN package instead of common, I think it's better to
start with building things specific to our current use case. Then, if we have
need of this code from another spot (eg MapReduce HA) we can consider moving it
to common. But let's not overly generalize until we have to -- eg from what
I've heard about MR HA, it stores all of its critical state in ZooKeeper so
this sort of fencing is not necessary.
> HA: namenode fencing mechanism
> ------------------------------
>
> Key: HDFS-2179
> URL: https://issues.apache.org/jira/browse/HDFS-2179
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: name-node
> Reporter: Todd Lipcon
> Assignee: Todd Lipcon
> Fix For: HA branch (HDFS-1623)
>
> Attachments: hdfs-2179.txt, hdfs-2179.txt, hdfs-2179.txt
>
>
> In an HA cluster, when there are two NNs, the invariant that only one NN is
> active at a time has to be preserved in order to prevent "split brain
> syndrome." Thus, when a standby NN is transition to "active" state during a
> failover, it needs to somehow _fence_ the formerly active NN to ensure that
> it can no longer perform edits. This JIRA is to discuss and implement NN
> fencing.
--
This message is automatically generated by JIRA.
For more information on JIRA, see: http://www.atlassian.com/software/jira
